The purpose of this study was to examine the pattern of the relationships among motivational beliefs and science achievement of 8th grade Taiwanese students, given that the students in Taiwan have high science academic achievement but low motivational beliefs in science learning on a series of international large-scale assessments. Three motivational beliefs in science learning, including self-concept, intrinsic value, and utility value, were conceptualized based on the modern expectancy-value theory. Data are from the Taiwanese proportion of the Trends in International Mathematics and Science Study 2011 dataset. Three groups of students, namely, the total group, the high-achieving group (HAG), and the low-achieving group (LAG), were examined. Results showed that the patterns of the relative predictions of motivational beliefs to science achievement were distinct for each group. In the total group, all the motivational beliefs could positively predict science achievement (R 2 = 20%). On the other hand, self-concept could positively and negatively predict science achievement for the HAG and LAG students, respectively, and intrinsic value could positively predict science achievement for the LAG students. In conclusion, this study, based on the Taiwanese representative sample, contributes to the discussion regarding national variation in students’ motivational beliefs and provides empirical-based evidence of the motivational beliefs in science learning of students of different levels of ability.